Twisted string actuator systems

ABSTRACT

A twisted string actuator system includes a motor generating rotary motion of a rotor and a twisted string comprised of a pair of cords. One end of the twisted string is attached to the rotor and an opposite end of the twisted string is coupled to a load. The cords are twisted about each other for a first section of the twisted string and untwisted for a second section of the twisted string. A cord guide is fixedly disposed between the cords. The first and second sections of the twisted string are on a first side and second side, respectively, of the cord guide. Rotary motion of the rotor in one direction operates to twist the pair of cords on the first side of the cord guide while pulling a portion of the pair of cords from the second side of the cord guide into the first side.

RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 14/458,283 filed Aug. 13, 2014, titled “Multilayer ElectrolaminateBraking System,” which is a continuation application of U.S. applicationSer. No. 14/005,092 filed Oct. 18, 2013, titled “Mobile RoboticManipulator System,” now U.S. Pat. No. 8,833,826, issued Sep. 16, 2014,which is the national stage of International Application No.PCT/US2012/029860, filed Mar. 21, 2012, designating the United States,which claims priority to and the benefit of the filing date of U.S.provisional application No. 61/454,945, filed on Mar. 21, 2011, titled“Improved Twisted String Actuator—I”, U.S. provisional application No.61/454,948, filed on Mar. 21, 2011, titled “A Modular RoboticAppendage—“A Finger””, U.S. provisional application No. 61/466,900,filed on Mar. 23, 2011, titled “Improved Twisted String Actuator—II”,and U.S. provisional application No. 61/466,902, filed on Mar. 23, 2011,titled “A Mobile Robotic Manipulator System”, the entireties of whichapplications are incorporated by reference herein.

GOVERNMENT RIGHTS IN THE INVENTION

This invention was made with government support under Contract No.W91-CRB-10-C-0139 awarded by the US Army. The government has certainrights in this invention.

FIELD OF THE INVENTION

The invention relates generally to robotic manipulator systems. Morespecifically, the invention relates to robotic appendages.

BACKGROUND

Many applications can benefit from the use of dexterous robotic handsthat are capable of performing human-like tasks, such as grasping andmanipulating a wide variety of objects. To achieve such versatility, thedevelopment of such robotic hands has turned to the use of underactuatedfingers because underactuated fingers can self-adapt to wrap aroundobjects, especially unknown objects. Although effective for powergrasps, however, underactuation may perform poorly in precision grasps,in which the positions of the fingertips need to be controlledaccurately, and where contact points are limited to distal links.

SUMMARY

In one aspect, the invention relates to a robotic finger assemblycomprising a finger skeleton with one or more joints, a motor generatingrotary motion of a rotor, and a twisted string comprised of a pair ofcords. One end of the twisted string is attached to the rotor and anopposite end of the twisted string is coupled to the finger skeleton.The cords are twisted about each other for a first section of thetwisted string and untwisted for a second section of the twisted string.A cord guide is fixedly disposed between the cords. The first section ofthe twisted string is on a first side of the cord guide, and the secondsection of the twisted string is on a second side of the cord guide.Rotary motion of the rotor in one direction operates to twist the pairof cords on the first side of the cord guide while pulling a portion ofthe pair of cords from the second side of the cord guide into the firstside of the cord guide.

In another aspect, the invention relates to a robotic finger assemblycomprising a finger skeleton with a pair of pulleys having a common axisof rotation, each pulley having a non-circular shape, a motor forgenerating rotary motion of a rotor, and first and second twisted stringactuators each including a twisted string coupled at one end to therotor and attached at an opposite end to one of the non-circularpulleys. The twisted string actuators are configured to operate in anantagonistic manner such that one twisted string actuator lengthens thetwisted string of that twisted string actuator while the other twistedstring actuator shortens the twisted string of that twisted stringactuator in response to rotary motion produced by the motor. Thenon-circular shape of the pulleys is adapted to keep both twistedstrings in tension throughout a range of the rotary motion produced bythe motor.

In yet another aspect, the invention relates to a twisted stringactuator system comprising a motor for generating rotary motion of arotor, a pair of cams having a common axis of rotation, each cam havinga non-circular shape, and first and second twisted string actuators eachincluding a twisted string coupled at one end to the rotor and attachedat an opposite end to one of the non-circular cams. The twisted stringactuators are configured to operate in an antagonistic manner such thatone twisted string actuator lengthens the twisted string of that twistedstring actuator while the other twisted string actuator shortens thetwisted string of that twisted string actuator in response to rotarymotion produced by the motor. The non-circular shape of the cams isadapted to keep both twisted strings in tension throughout a range ofthe rotary motion produced by the motor.

In still another aspect, the invention relates to a twisted stringactuator system including a motor generating rotary motion of a rotorand a twisted string comprised of a pair of cords. One end of thetwisted string is attached to the rotor and an opposite end of thetwisted string is coupled to a load. The cords are twisted about eachother for a first section of the twisted string and untwisted for asecond section of the twisted string. A cord guide is fixedly disposedbetween the cords. The first section of the twisted string is on a firstside of the cord guide and the second section of the twisted string ison a second side of the cord guide. Rotary motion of the rotor in onedirection operates to twist the pair of cords on the first side of thecord guide while pulling a portion of the pair of cords from the secondside of the cord guide into the first side of the cord guide.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of this invention may be betterunderstood by referring to the following description in conjunction withthe accompanying drawings, in which like numerals indicate likestructural elements and features in various figures. The drawings arenot necessarily to scale, emphasis instead being placed uponillustrating the principles of the invention.

FIG. 1 is a diagram of an embodiment of robotic manipulator (or hand)having four finger modules.

FIG. 2 is a side view of one embodiment of the robotic manipulator.

FIG. 3 is a front view of the embodiment of the robotic manipulator ofFIG. 2.

FIG. 4 is a view of an embodiment of the robotic manipulator with thefinger modules in an opposed configuration.

FIG. 5 is a view of an embodiment of the robotic manipulator with thefinger modules in a spherical configuration.

FIG. 6 is a view of an embodiment of the robotic manipulator with thefinger modules in an interlaced configuration.

FIG. 7 is a view of an embodiment of the robotic manipulator withunderactuated fingers grasping an object.

FIG. 8 is a view of an embodiment of the robotic manipulator withunderactuated fingers grasping a flashlight.

FIG. 9 is a view of the robotic manipulator with the fingers grasping asphere.

FIG. 10 is a view of an embodiment of the robotic manipulator with thefingers using a precision grasp to pinch a key.

FIG. 11 is a view of an embodiment of the robotic manipulator with thefingers using a precision grasp to hold a pencil.

FIG. 12A and FIG. 12B are diagrams of example modes of operation forfingers grasping an object.

FIG. 13 is a diagram showing the use of selective locking of the jointsof two opposing fingers to perform a precision grasp on a sphericalobject.

FIG. 14 is a diagram showing the use of selective locking of the jointsof two opposing fingers to perform a precision grasp on a flat object.

FIG. 15A and FIG. 15B are diagrams showing the use of selective lockingof the joints of two opposing fingers to hold, manipulate, and re-graspan object.

FIG. 16 is an exploded view of one embodiment of the robotic manipulatorincluding four finger modules and a palm assembly.

FIG. 17 is a side view of an embodiment of a finger module including afinger assembly mounted to an actuator module.

FIG. 18 is a view of an embodiment of the actuator module of FIG. 17.

FIG. 19 is a diagram of an exploded view of one embodiment of the fingermodule including the finger assembly and the actuator module.

FIG. 20 is a diagram illustrating an example of a measure of rotationalcompliance of the finger assembly.

FIG. 21 is a diagram illustrating an example of a measure of lateralcompliance of the finger assembly.

FIG. 22 and FIG. 23 are opposite side views of an embodiment of a fingerassembly.

FIG. 24 is a bottom view of the embodiment of the finger assembly ofFIG. 22 and FIG. 23.

FIG. 25 is an exploded view of one embodiment of the finger assembly.

FIG. 26 is an isometric view of one embodiment of the internal structureof the finger assembly.

FIG. 27 is an edge view of the internal structure of the fingerassembly.

FIG. 28 is a side view of an embodiment of the finger assembly with itsdistal joint shown in detail.

FIG. 29 is a diagrammatic view of an embodiment of a multilayerelectrolaminate structure.

FIG. 30 is a flow diagram of an embodiment of a process for assembling abrake subsystem of the finger assembly.

FIG. 31A-FIG. 31G are pictorial illustrations of example steps of theassembly process described in FIG. 30.

FIG. 32 is a diagrammatic representation of a multilayer skin covering aphalange of the finger assembly.

FIG. 33 is a diagram of an embodiment of a skin layer comprised ofelectroadhesive pads and embedded electrodes.

FIG. 34 is an image of an embodiment of a sensor assembly integratedinto a single flex circuit board.

FIG. 35 is a diagram illustrating a conventional twisted-stringactuator.

FIG. 36 is a diagram illustrating a twisted string actuator with a pinor pulley.

FIG. 37 is a diagram illustrating an embodiment of antagonistic stringactuators with non-circular cams.

FIG. 38 is a graph illustrating an example length of the cord that istwisted for each angular position of the motor.

FIG. 39 is an example graph of the effective moment arm for each angularposition of the motor.

FIG. 40 is an example graph illustrating the effective moment arm inpolar coordinates.

FIG. 41 is a diagram illustrating an example process of determining ashape of the non-circular cam radius.

FIG. 42 shows equations for computing an example shape of thenon-circular cam.

FIG. 43 is a graph illustrating an example shape of the non-circularcam.

DETAILED DESCRIPTION

Embodiments of robotic manipulators (or simply robotic hands) describedherein employ selective underactuation, compliant force control, andmultimodal tactile, position, and force sensing. Underactuation, whenapplied a mechanical device, signifies that the device has feweractuators than degrees of freedom. Controllable selectiveunderactuation, as described below, enable a robotic hand to graspunknown objects using a power grasp, and then to switch to a precisiongrasp in order to perform operations requiring fine control of fingertipposition and force. In general, a power grasp involves the palm andfingers in combination to secure an object firmly in the hand, whereas aprecision grasp involves the fingertip regions to control the pose of anobject precisely. With controllable selective underactuation, a robotichand can employ a combination of power and precision grasps to hold,manipulate, and reposition an object, a process referred to asre-grasping.

The capabilities of the robotic hand extend from the capabilitiesdesigned into its individual underactuated fingers. In brief overview,the joints of each underactuated finger can lock and unlockindependently in response to an electrical signal. This selectivelocking of joints allows a single actuator to multiplex the flexing ofthe finger joints. For example, each underactuated finger can passivelywrap around an object of unknown shape to cooperate in a power grasp,and then selected joints of the fingers can be locked so the fingers cancooperate in a pincer to perform a precision grasp. A transmissionintegrated into each underactuated finger is backdriveable and hasbuilt-in elasticity, making the robotic hand resistant to shock andoverload.

Grasping surfaces (i.e., skin) of the fingers can be fitted withelectroadhesive pads to control adhesion and generate friction forcesthat overcome slippage and enhance the hand's grasping capabilities, yetwithout having to exert a gripping force that could crush or damage theobject. The skin is abrasion-resistant and controllably compliant; thefinger can be “soft” when making contact with objects of unknown shapeand structure, and firm to control its precision precisely after makingcontact. Sensor assemblies integrated in the skin can sense contactpressure, slippage, and vibration. Fingers can detect contact points,grasping and pinching forces, the stability of the object, and slippage.These abilities enable manipulation and re-grasping of objects byrolling and sliding objects between fingertips. Other sensor devices canbe incorporated into the finger to sense other types of parameters, forexample, temperature and pressure.

FIG. 1 is a diagram of an embodiment of a robotic hand 10 having fourfinger modules 12-1, 12-2, 12-3, 12-4 (generally, 12) coupled to a palmassembly 14. Each finger module 12 comprises a finger assembly (orsimply finger) 16 with a proximal joint 18-1, an intermediate joint18-2, and a distal joint 18-3. The proximal joint 18-1 couples aproximal phalange 20-1 to a finger mount 24, the intermediate joint 18-2couples an intermediate phalange 20-2 to the proximal phalange 20-1, andthe distal joint 18-3 couples a distal phalange 20-3 (also called thefingertip) to the intermediate phalange 20-2. The finger mount 24 ispart of an actuator module, described in detail below. Each finger 16has multilayer skin 22. The palm assembly 14 can also be covered in a‘skin’ adapted for grasping objects.

Each finger 16 can flex forward or backward at any of the joints and hasthree degrees of freedom (DOF); although the finger can have fewer ormore DOFs, depending upon the particular application. As described inmore detail below, a single actuator controls all three degrees of afinger, with selective locking of the joints allowing the singleactuator to multiplex the flexing of the joints, individually, or ingroups. By locking and unlocking the joints in rapid succession, thejoints can appear to move and be controlled simultaneously.

In this embodiment, the finger modules 12-1, 12-2 are movably coupled toone side of the palm assembly 14, and the other finger modules 12-3,12-4 are fixed in position to the opposite side of the palm assembly 14.The finger modules 12-1, 12-2 can move together or apart. Fixing thelocation of the other finger modules 12-3, 12-4, makes their locationsknown and predictable, which is advantageous for precision graspsinvolving pinching by opposing finger modules (e.g. 12-1 and 12-4).

Although described herein with reference to robotic hands with fourfingers, the principles can extend to those embodiments with fewer ormore than four.

FIG. 2 and FIG. 3 show a side view and front view, respectively, of oneembodiment of the robotic hand 10 extending from a forearm 30. Eachfinger 16 has a protective fingernail 32 at its fingertip. Thefingernails of opposing fingers can be used to grasp small edges.

FIG. 4, FIG. 5, and FIG. 6 show the robotic hand 10 in three differentconfigurations. In FIG. 4, the fingers 16-1, 16-2 are directly opposedto the fingers 16-3, 16-4 (finger 16-1 being directly opposite finger16-4; finger 16-2 being directly opposite to finger 16-3). In thisconfiguration, the finger modules 12-1, 12-2 are together, adjacent toeach other, approximately midway along the side of the palm assembly 14.The fingers 16 are bent so that the distal phalanges 20-3 andintermediate phalanges 20-2 of the fingers 16-1 and 16-4 are parallel toeach other; as are the distal 20-3 and intermediate phalanges 20-2 ofthe fingers 16-2 and 16-3. The finger modules 12-1, 12-2 are disposed ina track 40 along which the finger modules 12-1, 12-2 can travellaterally along the side of the palm assembly 14. This lateral movementcapability of the finger modules 12-1, 12-2 makes the anatomy of therobotic hand 10 dynamically reconfigurable.

In FIG. 5, the fingers 16-1, 16-2 are spatially apart from each otherand arched toward the other fingers 16-3, 16-4, which arch back towardthe fingers 16-1, 16-2. The arrangement produces a spherical pose amongthe fingers 16. In FIG. 6, the fingers 16-1, 16-2 are spatially apartfrom each other at opposite ends of the track 40 and bent forward. Theother fingers 16-3 and 16-4, fixed in their positions on the oppositeside of the palm assembly 14, are also bent forward, extending in theopposite direction of and coming in between the bent fingers 16-1 and16-2, producing an interlaced arrangement among the fingers 16.

FIG. 7 through FIG. 11 show different grasps of which the robotic hand10 is capable. The different grasps presented are merely illustrativeexamples; many other types of grasps are possible. In FIG. 7, theunderactuated fingers are executing a power grasp of an irregularlyshaped object 50. FIG. 8 shows the underactuated fingers in aninterlaced configuration grasping a flashlight 52. FIG. 9 shows thefingers in a spherical configuration grasping a sphere 54. Two of thefingers use a power grasp to pinch a key 56 in FIG. 10, whereas, in FIG.11, two fingers use a precision grasp to pinch a pencil 58.

FIG. 12A and FIG. 12B show the use of selective locking of the joints oftwo opposing fingers 16-1 and 16-4 to alter a grasp of an object 60. InFIG. 12A, with all of the joints 18-1, 18-2, 18-3 (generally, 18)unlocked, the fingers conform to the shape of the object 60, and therobotic hand 10 performs a power grasp. Initially, the fingers 16 canclose about the object until a finger detects light contact with theobject. When a finger detects contact, its proximal joint 18-1 can belocked, while the remaining intermediate and distal joints of the fingerremain unlocked. The intermediate and distal joints can continue to flexwithout increasing the contact force applied to the object. Accordingly,the contact with the object causes minimal disturbance of the object.Subsequently, the intermediate joint 18-2 can be locked, for example,after contact is detected on the intermediate phalange 20-2, while thedistal joint 18-3 remains unlocked. By locking the proximal andintermediate joints 18-1, 18-2, force can be transferred force to distaljoint 18-3, and the finger 16 has thus progressed from beingunderactuated with three degrees of freedom to having a single degree offreedom. After each finger makes contact sufficient to establish a graspof the object, all joints can be locked to stiffen the grasp, as shownin FIG. 12B.

FIG. 13 shows the use of selective locking of the joints of two opposingfingers 16-1 and 16-4 to perform a precision grasp on a spherical object62, which is held between the fingertips. In the execution of thisgrasp, the proximal joints 18-1 of both fingers are unlocked, while theintermediate joints 18-2 and distal joints 18-3 of both fingers 16-1,16-4 are locked, which effectively locks their distal phalanges 20-3.

FIG. 14 shows the use of selective locking of the joints of two opposingfingers 16-1 and 16-4 to perform a precision grasp on a flat object 64.The distal phalanges 20-3 of the opposing fingers can hyperextend toform a flat gripper, which provides a simple way of grasping smallobjects. To hold the object, all of the joints can be unlocked.

FIG. 15A and FIG. 15B show the use of selective locking of the joints oftwo opposing fingers 16-1 and 16-4 to hold, manipulate, and re-grasp anobject 66. In FIG. 15A, the robotic hand has the object in a precisiongrasp, with the proximal joints 18-1 and intermediate joints 18-2 ofboth fingers being unlocked, while the distal joints 18-3 of bothfingers are locked. As shown in FIG. 15B, in an attempt to rotate theobject 66, the distal phalange 20-3 of the finger 16-1 pushes upwardsagainst the object 66 and then locks its intermediate joint 18-2,momentarily holding the finger 16-1 in this present position so that theother finger 16-4 can make the next move to further the rotation. Bymultiplexing incremental acts of flexing, locking, unlocking, andcombinations thereof, the fingers can cooperate to manipulate andre-grasp objects held by the fingers 16 of the hand 10.

FIG. 15A and FIG. 15B are just one example of how the robotic hand 10can re-grasp an object. Numerous other techniques are possible, forinstance, using three fingers to hold an object in a power grasp, whilea fourth finger moves the object held in the power grasp. For example,the robotic hand 10 can use three fingers to hold a flashlight in apower grasp, and a fourth finger to rotate the flashlight to find andpress its on/off button.

FIG. 16 shows an exploded view of one embodiment of the robotic hand 10including the four finger modules 12-1, 12-2, 12-3, 12-4 and the palmassembly 14. All finger modules 12 are modular in construction; they areinterchangeable, and can either be fixed or movably coupled to the palmassembly 14. In one embodiment, the palm assembly 14 includes a palm 68,a motor-and-hand controller PCB (printed circuit board) stack 70, adivider 72, a finger-spreader motor 74, a finger-spreader actuator 76,two finger-spreader blocks 78, a finger-module mount 80, high-voltageelectronics 82, a base housing 84, and an arm adapter 86.

The arm adapter 86 couples the robotic hand 10 to a robotic forearm, forexample, a GFE Barrett Arm (not shown). The base housing 84 attaches tothe raised surface of the arm adapter 86. The high-voltage electronics82 are housed within the base housing 84 and distribute power to thefinger modules 12, motor-and-hand controller stack 70, andfinger-spreader motor 74. In particular, the high-voltage electronics 82include multiple switchable channels of high voltage (±1 kV) used toselectively lock and unlock joints 18, as described in more detailbelow.

The finger-spreader actuator 76 mounts to the open side of the fingermodule mount 80, and the finger module mount 80 connects to the topsurface of the base housing 84. The finger-spreader motor 74 resideswithin a compartment defined by the side wall of the finger module mount80 and the finger-spreader actuator 76. The finger-spreader motor 74 isoperably coupled to move the finger-spreader actuator 76. The fingermodules 12-3, 12-4 attach to the exterior of the side wall of fingermodule mount 80. Each finger-spreader block 78 couples one of the otherfinger modules 12-1, 12-2 to the finger-spreader actuator 76.

The palm 68 houses the motor-and-hand controller stack 70 and attachesto the top of the finger-module mount 80, the divider 72 serving as agasket between the palm 68 and finger-module mount 80. Themotor-and-hand controller stack 70 controls operation of thefinger-spreader motor 74 in response to control commands, and interfaceswith the finger modules 12 and the high-voltage electronics 82. Controlsignals sent from the motor-and-hand controller stack 70 to thehigh-voltage electronics 82 control the use of electroadhesion in theskin of the fingers and switch high voltage (e.g., +1 kV; −1 kV) amongthe electrolaminate brakes used to selectively lock and unlock thefinger joints 18.

FIG. 17 shows an embodiment of a finger module 12 including the fingerassembly 16 mounted to an actuator module 90. The actuator module 90provides a backdriveable, twisted-string transmission with built-incompliance and low backlash. Although shown to be integrated into thefinger module 12, in other embodiments, the twisted-string transmissionof the actuator module 90 can be implemented in or mounted on a forearmconnected to the robotic hand 10.

The actuator module 90 houses a motor 92, a machined spring 94, a motorencoder 96, a twisted string 98, a Hall Effect sensor 100, and a sensorcircuit board 102 with a controller (e.g., 80 MIPS DSP). The motor 92is, in one embodiment, a brushless DC motor (e.g., 15 W) with a highgear ratio (i.e., greater than 50:1). The motor encoder 96 tracks theposition of the motor 92. The twisted string 98 is coupled by the fingermount 24 to the drive tendon 130. The twisted string 98 can be a KEVLAR,Spectra, or Vectran cable. The Hall Effect sensor 100 measurescompression of the twisted string 98 to provide a force feedback signal,and the controller and sensor board 102 includes a force/current sensorthat can measure actuator torque.

In brief overview, the actuator module 90 translates rotary motion ofthe motor 92 to linear motion of a tendon 130 (FIG. 22) within thefinger 16. The motor 92 twists the twisted string 98. Twisting motion inone direction causes the length of the twisted string 98 to shorten,which causes a pull of the tendon 130 through the finger, causing thefinger to actuate. The finger 16 flexes accordingly depending on whichjoints are locked and unlocked. Twisting in the other direction releasescompression on the twisted string 98; and the spring return 140 (FIG.24) urges the finger 16 to extend in a manner depending on which jointsare presently locked and unlocked.

With a backdriveable transmission, the actuator module 90 can beresponsive to external disturbances and maintain the force exerted onthe finger below a certain level. If active force control is used tobackdrive the transmission, sensors measure external forces exerted onthe finger 16, and provide feedback. In response to this feedback, theactuator module 90 actively causes the motor 92 to move the finger in amanner as though the external forces were pushing the finger. Thus, thefinger does not wholly resist the external forces, but moves with them.Alternatively, the transmission can be passively backdriveable without asensor or a closed feedback loop buy using a low gear ratio (below 1:50)and having high efficiency.

FIG. 18 shows an embodiment of the actuator module 90 of FIG. 17. Theactuator module 90 has disc-shaped plates 104 that interleave with andcouple to plates of a finger assembly 16, to form the proximal joint18-1 (FIG. 1) of the finger assembly 16. One side of the actuator module90 has a notch 106 adapted to mount to one side of the palm assembly 14(either to a rail on the side wall of the finger module mount 80 (FIG.16) or to the finger-spreader blocks 78 (FIG. 16)).

FIG. 19 shows an exploded view of one embodiment of a finger module 12including the finger assembly 16 and the actuator module 90 (explodedinto three pieces: a plastic housing 90A, a palm assembly mount 90B withthe notch 106, and a cover 90C). Also shown are the motor 92, themachined spring 94, the motor encoder 96, the sensor board 102, aforced-sensor assembly 110, and a twisted string assembly 112 with thetwisted string 98. In addition, a flat flex electrical circuit 114extends from the actuator module 90 to the proximal joint 18-1. The flexcircuit 114 contains the communication bus for the position and tactilesensors in the fingers.

FIG. 20 and FIG. 21 show examples of mechanical compliance provided bythe finger mount 24 used to join the finger assembly 16 to the actuatormodule 90. FIG. 20 shows to what degree the finger assembly 16 can betwisted relative to the actuator module 90. In this example, the fingermodule 20 is designed for ±15 degrees of twisting with respect to axis120. FIG. 21 shows a measure of lateral compliance of the fingerassembly 16 relative to the actuator module 90. Measured with respect tothe axis 122, the finger assembly can tilt ±15 degrees. A flexurefeature in the proximal joint 18-1 in the finger mount 24 at the base ofthe finger assembly 16 provides the rotational compliance. When anobject is grasped with multiple fingers, the rotational and lateralcompliance of the fingers can ensure that the fingers passively alignand balance the normal forces exerted on the object.

FIG. 22 and FIG. 23 show opposite side views of an embodiment of thefinger assembly 16. In FIG. 22, the finger assembly 16 includes a singlecable (referred to as the tendon) 130 extending the length of the fingerassembly. The tendon 130 runs from the finger mount 24 (not shown),routes around each joint 18-1, 18-2, 18-3, passes through each phalange20-1, 20-2, and 20-3, and terminates near the fingertip 32 at an anchorpoint 132, to which the tendon 130 is fixed. The route of the tendon 130through the finger 16 around the joints 18 and phalanges 20 runs tangentto pulley surfaces and passes through arcuate channels 134; the route issmooth, having no sharp corners. To bend the finger 16, force is appliedto the tendon 130 in the direction indicated by arrow 136. The shapeassumed by the finger 16 in response to the applied force depends onwhich joints 18 are locked and unlocked (and on any object currently inthe grasp). FIG. 23 shows the side of the finger 16 opposite the tendon130. In FIG. 23, the finger 16 has a thin protective outer skin 138,with accordion-like folds at the joints 18 to allow for bending.

FIG. 24 shows a bottom view of the embodiment of the finger assembly 16with a spring return 140 extending from the finger mount 24 to thedistal phalange 20-3. The spring return 140 couples to the finger mount24 and to each phalange 20-1, 20-2, and 20-3 at anchor points 142. Thespring return 140 generally opposes the tendon 130 and urges the finger16 to extend (straighten). Although a single tendon is being used toflex the finger, with a spring return 140 to urge the finger 16 back toits extended position, other embodiments can omit the spring return anduse a single tendon in a loop configuration around the pulleys, or usemultiple tendons.

FIG. 25 shows an exploded view of one embodiment of various componentsin the finger assembly 16. The components include a stamped sheet metalskeleton 150, a flex circuit 152 pre-bonded to the skeleton 150,injection molded cable pulleys 154-1, 154-2, and 154-3 (generally, 154),a first portion of an injection molded core 156, a brake subsystem 158,a stamped sheet metal skeleton 160 with hollow pins 162, a secondportion of the injection molded core 164 with the tendon 130pre-inserted, the elastic spring return 140, and rivets 166.

When the finger 16 is fully assembled, the flex circuit 152 folds aroundeach phalange 20. The tendon 130 runs over the cable pulleys 154. Thetwo portions of the injection molded core 156, 164 attach to each otherto contain the tendon 130. The spring return 140 attaches to anchorpoints 142 of the exterior side of the second portion of the injectionmolded core 164.

The brake subsystem 158 provides the ability to lock and unlock joints.The brake subsystem 158 is shown here as a pre-assembled unit.Alternatively, the brake subsystem 158 can be assembled on the skeleton.The hollow pins 162 extend through openings in the brake subsystem 158,the pulleys 154, and skeleton 150. The ends of the hollow pins 162 areflared to secure the assembly. The rivets 166 secure the skeleton 160 tothe brake subsystem 158.

FIG. 26 shows an isometric view and FIG. 27 shows an edge view of theinternal structure of the finger 16 after assembly. The multi-layerinternal structure includes the brake subsystem 158 sandwiched betweenthe two sheet metal skeletons 150, 160. Segments of the brake subsystem158 are wrapped in a shielding layer 170. The shielding layer 170shields sensors (i.e., in the flex circuit 152) from possibleinterference from the high-voltage locking and unlocking actuation ofthe joints 18.

FIG. 28 shows an example of the finger assembly 16, with its distaljoint 18-3 shown in detail. The distal joint 18-3 includes the cablepulley 154-3 and a multilayered composite structure 180 made ofelectrolaminate materials. In general, electrolaminates change fromcompliant and spring-like to essentially rigid, using electrostaticclamping to control the connectivity between different materials in thelayered composite structure. The electrolaminate structure can withstandslip under pressure. The maximum force that the compositeelectrolaminate structure 180 can withstand is a function of theproperties of the clamping surfaces, the applied voltage, and the totalclamping area. Typical maximum clamping pressures are about 0.4 Mpa (70psi).

The multilayered composite electrolaminate structure 180 can befabricated as a monolithic sheet 190 (FIG. 31A) with individualattachment points to each joint (or set of joints) that can be locked.The multilayered composite electrolaminate structure 180 includespassive (voltage-off) compliant elements that operate to oppose theactuator tendon 130 and provide an extensional force for each joint 18.The multilayered composite electrolaminate structure 180 can be shieldedby locating the ground planes on the outermost electrodes, or byencircling the electrolaminate structure 180 in a conductive elastomericsheath.

FIG. 29 shows a diagrammatic representation of a multilayerelectrolaminate structure 180 to illustrate the stiffening operation ofa joint 18. The multilayer electrolaminate structure 180 includes aplurality of brake layers 182 interleaved with spacer layers 184. Thejoint 18 rotates about axis 186. In response to an electrical signal(i.e., high voltage) to lock this joint 18, the pressure distribution onthe multilayer structure 180 occurs on both sides of the structure asillustrated by arrows 188. Rather than concatenate segments of themultilayer electrolaminate structure 180 end-to-end, the multilayerelectrolaminate structures 180 can be overlapped at the joint 18 toallow individual joint locking. Each segment of multilayerelectrolaminate structure 180 is independently drivable; locking can beapplied to the distal joint only, to the intermediate joint only, to theproximal joint only, to any two joints concurrently, or to all jointsconcurrently.

The multilayer electrolaminate structure 180 generates pressure throughelectrostatics, and is capable of producing high locking torques (e.g.,approximately 4-12 lb-in for an electrolaminate stiffener having 5layers, a 0.25 to 0.50 inch diameter, and 0.25 inch total thickness, andweighing 2.5 g). Power consumption can be less than a tenth of a Watt(e.g., 0.06). All forces are internal; hence the brake subsystem 158does not require an external rigid structure to apply the braking force.After the applied voltage is removed, the multilayer electrolaminatestructure 180 releases its grip in approximately 10 ms to 500 ms. Therelease time can determine how quickly one can multiplex locking andunlocking among the joints 18 of a finger 16.

FIG. 30 shows a flow diagram of an embodiment of a process 200 forassembling the brake subsystem 158 of the finger assembly 16. In thedescription of the process 200, reference is made to FIGS. 31A-31G toprovide pictorial illustrations of some of the steps of the process 200.At step 202, an electrolaminate sheet 190 (FIG. 31A) is pre-folded intoan accordion pattern 192 (FIG. 31B). Shielding layers 170 (FIG. 31C) arewrapped (step 204) around the electrolaminates. The accordion pattern192 is placed (step 206) onto rods 194 (FIG. 31D), the rods 194 aligningwith mounting features 196 on the finger skeleton 160. The brake layers182 are interlaced (step 208) at each joint 18 and the accordion pattern192 is lowered (step 210) onto the skeleton. The electrolaminates aresecured (step 212) with the other side of the skeleton 150. High voltagewires 198 are attached (step 214) to the electrolaminates, to carry avoltage to each joint 18 that causes the corresponding multilayerelectrolaminate structure of that joint to stiffen.

FIG. 32 shows a representation of the multilayer skin 220 covering aphalange 20 of the finger assembly 16. The multilayer skin 220 includesa protective outer layer 222, an electroadhesive layer 224, ashield-compliant layer 226, and a sensor layer 228. The protective outerlayer 222 wraps around the finger 16 to protect its internal componentsfrom external elements, such as dust, moisture, and chemicals. Theprotective outer layer 222 is made of a compliant and abrasion-resistantmaterial, for example, polyurethane or latex. The material provides highfriction, tear resistance, stretch-ability, and overall durability. Theprotective outer layer 222 is replaceable should it become worn fromuse.

The electroadhesive (EA) layer 224 is an electrically controllable skinlayer capable of adhering to many materials surfaces, producing theeffect of variable skin friction. This friction can assist in grippingobjects to overcome slippage and enhance grasping capability. The EAlayer 224 enables grasping objects of various sizes, with lower graspingforces, by controlling traction and sliding. The EA layer 224 can clampon many types of materials, including, but not limited to, glass, wood,metal, concrete, drywall, brick, and granite. The clamping forces varywith the material. In addition, the EA layer 224 consumes almost nopower (e.g., 0.02 mW/N of weight supported). The EA layer 224 can bedetachable without affecting the mechanical grasping capabilities of thefinger. The detachability enables use of the EA layer 224 whenever theEA layer 224 is appropriate for the task.

In one embodiment, the EA layer 224 is implemented with electroadhesivepads 230 (FIG. 33) with embedded electrodes 232 (FIG. 33). The EA layer224 can be fabricated with a polymer, using a deposition technique, suchas spray patterning. The electrode pattern can be fabricated fromsilicone or vulcanized rubber. A thin layer of abrasion-resistantpolymer is deposited over the patterned electrodes to embed theelectrodes. Although shown in FIG. 33 to be implemented on the phalangesof the fingers and on the palm, the EA layer 224 can also be folded intothe joints.

High voltage (low current) applied to the electrodes induceselectrostatic charges on the skin surface, which introduces anti-slipforces along an object surface. These anti-slip forces (or shear ortraction forces) are decoupled from normal forces, enabling independentcontrol of the normal and shear forces. This independent control isparticularly advantageous for purposes of re-grasping an object. Theselective modulation and enhancement of the skin friction (without theneed for high grasping forces and tolerances) can be used in cooperationwith object manipulations. Electroadhesion is described in more detailin U.S. Pat. No. 7,553,363, U.S. application Ser. No. 12/830,239, andU.S. application Ser. No. 12/762,260, the entireties of which areincorporated by reference herein.

The shield-compliant layer 226 is an electrically conducting layerintegrated into one side of the EA layer 224 to mitigate interferencewith the various sensors of the tactile sensor layer 228 by theoperation of the EA layer 224.

The sensor layer 228 is comprised of a sensor assembly of tactilepressure sensors, vibrotactile sensors, and finger-joint positionsensors for sensing contact pressures, slippage, and vibration atfingertips. Other types of sensors can be integrated into the sensorlayer, including but not limited to shear sensors and temperaturesensors. In one embodiment, the sensor layer is integrated into a singleflex circuit board (e.g., flex circuit 152 of FIG. 25) that conforms tothe grasping surfaces of the finger 16. For sensing contact and sliding,the fingertip 32 has an accelerometer.

FIG. 34 shows an embodiment of a sensor assembly integrated into asingle flex circuit board 152′ (the prime (′) here signifying analternative embodiment of the flex circuit 152 shown in FIG. 25). Eachfinger 16 has the flex circuit board 152′, which extends to all fingerjoints 18 and phalanges 20. Position sensors 240 and tactile (pressure)sensors 242 are printed onto the flex circuit board 152. The positionsensors 240 are embedded in the joints 18; the tactile sensors 242 areon the phalanges 20. Types of position sensors include, but are notlimited to, capacitive sensors, Hall-Effect sensors, inductive sensors,and potentiometers. Preferably, the position sensor 240 includes arotary capacitive sensor array 244, as shown in FIG. 34, with a built-inshield layer 246. The shield layer 246 mitigates interference from theoperation of the brake subsystem 158 on the performance of the positionsensor 240.

The flex circuit board 152′ can further include a position sensor 248having a sensor array 250 and built-in shield 252. The sensor 248provides the position of each joint.

FIG. 35 shows a diagram generally illustrating a conventionaltwisted-string actuator 260, in which two cords 262 twist about oneanother, or about a core, to form a helical section that shortens as theinput (motor) is rotated. One end of this pair of cords 262 is attachedto the input rotating shaft (from a motor) and the other end isconnected to a sliding mechanism 264 that prevents this other end fromtwisting. This sliding component 264 is then attached to the output 266of the actuator 260, for example, a tendon or other similar linearoutput. The length of cord 262 between the sliding and rotating ends ofthe twisting section is fixed and prescribed by the designer.

In FIG. 36, the sliding component 264 is eliminated and, in its place, afixed pin 270 or pulley is used. The distance between the rotating inputshaft (of the motor) and the pin 270 is constant and fixed by thedesigner. As the actuator input (motor) 260 is rotated, the cords 262between the actuator input 260 and the fixed pin 270 twist, shorteningand pulling additional untwisted string past the fixed pin or pulleyinto the twisted region. In this manner, the length of the string thatis twisted is no longer fixed, but increases as the actuator input shaftrotates. Because a greater length of cord is available to be twisted, agreater number of twists can be supported before exceeding the limit ofthe critical helix angle, given byAlpha-max=arctan(number of cords×radius of cord/pi×radius of helix),

after which knotting occurs. For a two-cord actuator, this criticalhelix angle is about 32.5 degrees, where a 90-degree helix angledescribes an untwisted actuator. The use of the pin 270 (or pulley)increases the effective stroke of the actuator, allowing the cords 262to foreshorten by 86% of its original length, compared to 46% of a fixedlength cord, before this limit is reached. The length of the actuator atthe maximum helix angle, alpha max is:Linit/cos(pi−alpha max)−Linit

where Linit is the distance between the fixed pin or pulley and therotating input. Therefore, percent foreshortening is:(Linit/cos(pi−alpha max)−Linit/Linit=0.86

Further, in the conventional twisted string actuator 260 of FIG. 35, theoutput 266 is nonlinear. Furthermore, when a pair of twisted stringactuators is used in an antagonistic manner, for example, to move alever, or arm, around a pivot point, or joint, one actuator lengthenswhile the opposite one shortens, each in a non-linear manner. Therefore,if two tendons connected to the twisted string actuators were used toactuate a robot joint by wrapping the tendons around a circular pulleyat that joint, the tension in the tendons would change when the joint ismoved. In some joint positions the tendons would be slack and theposition of the joint would not be known and not be controlled.

To linearize the output action of a set of opposing, antagonistic,twisted string actuators 300-1, 300-2 (generally, 300), a non-circularpulley can be used, as shown in FIG. 37. Each tendon 302-1, 302-2 isfixed to a non-circular cam 304-1, 304-2, respectively, which share acommon axis 306 of rotation (enters into the plane of the FIG. 37 atcrosshairs). In FIG. 37, cam 304-1 is above the cam 304-2. Each of thetendons 302-1, 302-2 passes around an idler pulley 308-1, 308-2,respectively (in FIG. 37, idler pulley 308-1 is above idler pulley308-2). The tendon 302-1 is connected to the upper cam 304-1; the tendon302-2 crosses below the tendon 302-1 and is connected to the lower cam304-2.

A motor 310 turns the string actuator 300-1, which has gears 301-1 thatmesh with the gears 301-2 of the other twisted string actuator 300-2.The twisted string actuators 300 are antagonistic; the motor 310operates to turn them 300 in operate directions (as indicated by arrows312); alternatively, the motor 310 operates to turn them 300 in the samedirection, but the twisted string sections 314-1, 314-2 are twisted inopposite directions. In one embodiment, a fixed pin (or pulley) 315-1,315-2 can be disposed between the cords of each twisted string 314-1,314-2, respectively, to increase the length of cord that is availablefor twisting, as described in connection with FIG. 36.

The specific shape of each cam 304-1, 304-2 is determined algebraically.In the embodiment shown, each cam 304-1, 304-2 has a shape of anautilus; the cams 304 oppose each other (i.e., a mirror image of eachother). In this way, both tendons remain in proper tension as theactuator system moves through its designed range of operation.

Consider that the length of a cord 302 that will be twisted, L, is equalto 3.5 in., the diameter of 60 lb. test spectra cord, d, is equal to013·in.; the radius of the cord, r, is equal to d/2, and θ is theangular position of the motor 310.

As the cord 302 twists, its length depends on the angular position ofthe motor 310, given by the equation Length(θ):=L cos(asin((θ·r)/L)).The change in this length is given by the equationdLdθ(θ):=((θ*r²)/(L*sqrt(1−(θ²·r²)/L²)). FIG. 38 is a graph showing theshortening length of the twisted cord as a function of the angularposition of the motor 310.

Consider, for illustration purposes, that the cam 304 rotates 1/60^(th)of a full rotation for each full rotation of the motor 310 (i.e.,Ratio:=60), where the rotation of the cam, called OutputRotation, isequal to 360 deg/Ratio. The effective radius of the cam is given by theequation r₂:=Ratio*((θ*r²)/(L*sqrt(1−(θ²·r²)/L²)). FIG. 39 shows theeffective moment arm of the cord 302 around the axis 306 (i.e.,perpendicular distance from the axis 306 of rotation to the line of thecord) as a function of the angle of the motor. FIG. 40 is a graph, inpolar coordinates, of the effective moment arm as a function of theangle of the motor.

Consider further, for illustration purposes, that the radius of theidler pulley 308, r₄, is equal to 0.6113 in., and that the distance, S,between the center, C, of the idler pulley 308 and the cam axis 306 isequal to 2.0 in.

FIG. 41 graphically illustrates an algorithm by which to determinealgebraically the shape of the cams 304. In brief overview, thealgorithm finds the angle θ between the line connecting the center ofthe cam and the idler pulley for each angle φ. Phi, φ, is the rangevariable, and represents the orientation (angle) of the output cam. r(φ)is the instantaneous radius of action, which is at a right angle towhere the cord 302 tangentially contacts the cam 304. Then, thealgorithm finds the coordinates of points A and D. The algorithmincrements the angle to φ′, and get new points A′ and B′, and finds theintersection 320-1 of line AD and EF. The process repeats for eachincrement of the angle (e.g., the dotted and dashed iterations in FIG.41 are each an increment of the angle), finding a new intersection pointbetween the new tangential line and the previous tangential line. Thecurve formed by the intersection points 320-1, 320-2 corresponds to theshape of the cam 304. The equations for determining the shape are asfollows:θ(φ):=asin((r ₂(φ*Ratio)+r ₄)/S);[e.g.θ(φ)=22.242 deg]C(φ):=(S·cos(φ)S·sin(φ))(C is the center of the idlerpulley308,e.g.,C(φ)=(−20) in).

The vector from the center C of the idler pulley to the point oftangency A is:CA(θ,φ):=(r ₄*cos(θ+φ+π/2)r₄*sin(θ+φ+π/2));[e.g.,CA(θ(φ),φ=(0.231−0.566) in.]A(φ):=C(φ)+CA(θ(φ),φ;[e.g.,A(φ)=(−1.769−0.566) in.]D(φ):=(r ₂(φ*Ratio)*cos(θ(φ)+φ−π/2)r2(φ·Ratio)sin(θ(φ)+φ−π/2));[e.g.,where r ₂(φ·Ratio)=0.146in,D(φ)=(−0.055 0.135) in.]

The center C of the idler pulley is incremented by the angle ε (e.g.,ε:=0.1 deg.) to determine the next tangential line of the cord 302 andits point of intersection with the previous line.E(φ):=C(φ+ε)+CA(θ(φ+ε),φ+ε);[e.g.,E(φ)=(−1.768−0.569) in.]F(φ):=[r2[(φ+ε)·Ratio] cos(θ(φ+ε)+φ+ε−π/2),r2[(φ+ε)·Ratio]sin(θ(φ+ε)+φ+ε−π/2)];[e.g.,F(φ)=(−0.055,0.135) in.]

The algorithm finds the points of intersection:x1(φ):=|A(φ)⁽⁰⁾ /m|;x1=f(Unitless)→Unitlessy1(φ):=|A(φ)⁽¹⁾ /m|x2(φ):=|D(φ)⁽⁰⁾ /m|y2(φ):=|D(φ)⁽¹⁾ /m|x3(φ):=|E(φ)⁽⁰⁾ /m|y3(φ):=|E(φ)⁽¹⁾ /m|x4(φ):=|F(φ)⁽¹⁾ /m|y4(φ):=|F(φ)⁽¹⁾ /m|

FIG. 42 shows the equations for computing the output of the X(φ) andY(φ), which provides the shape of the cam corresponding by the points ofintersection.

The following describes an example of determining a range in the numberof twists needed in each twisted string section 314 (FIG. 37) tocomplete a desired range of rotation of a finger joint (each string willhave the same number of twists). For example, consider the desired rangeof rotation for the joint to be between −90° and +90° (i.e., total rangeof 180°, or π radians) with reference to a neutral position (i.e., themidpoint). For the cam output, φ, to go through this angle of π radians,the motor must go through Ratio*π radians, which is equal to 188.496total rotations of motor in radians. If the midpoint is given as anumber of twists (e.g., mid:=50) in each string, then mid·2·π=314.159 isthe number of radians the motor has spun to get this many twists. For arange centered at mid radians, rotating plus Ratio*π/2 radians and minusRatio*π/2 radians produces a minimum number of twists (min) and amaximum number of twists (max) to achieve the full desired range ofrotation (min:=mid*2*π−Ratio*π/2, and max:=mid*2*π+Ratio*π/2). In thepresent example, min=219.911 rad and max=408.407 rad, and thecorresponding radians of rotation for the motor are min/2−π=35 twistsand max/2−π=65 twists.

The orientation of the output cam at extremes of cable twists:min/Ratio=210 deg; and max/Ratio=390 deg.

A check of the total travel:(max−min)/Ratio=180 deg.

A check of that angle at mid-range of the travel:(mid·2·π)/Ratio=300 deg.Φ:=min/Ratio,min/Ratio+ε . . . max/Ratio.i:=0,1 . . . π/εOutput_(i,0) :=X(min/Ratio+ε*i)Output_(i,1) :=Y(min/Ratio+ε*i)

A check of the slope of a line between first and last point:atan((Output_(1800,1)−Output_(0,1))/(Output_(1800,0)−Output_(0,0)))=−12.693·deg.

Table 1 shows the cam Output (in.)=

TABLE 1 0 1 0 −0.173 0.06 1 −0.173 0.06 2 −0.173 0.06 3 −0.174 0.059 4−0.174 0.059 5 −0.174 0.059 6 −0.174 0.059 7 −0.174 0.058 8 −0.175 0.0589 −0.175 0.058 10 −0.175 0.058 11 −0.175 0.057 12 −0.175 0.057 13 −0.1750.057 14 −0.176 0.056 15 −0.176 . . .

FIG. 43 shows the output, which corresponds to the shape of the cam 304.The common axis 306 of the cam 304 is at the origin (0,0) of the graph.

Reference in the specification to “one embodiment” or “an embodiment”means that a particular, feature, structure or characteristic describedin connection with the embodiment is included in at least one embodimentof the teaching. References to a particular embodiment within thespecification do not all: necessarily refer to the same embodiment. Theterminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method, and computer programproduct. Thus, aspects of the present invention may be embodied entirelyin hardware, entirely in software (including, but not limited to,firmware, program code, resident software, microcode), or in acombination of hardware and software. All such embodiments may generallybe referred to herein as a circuit, a module, or a system. In addition,aspects of the present invention may be in the form of a computerprogram product embodied in one or more computer readable media havingcomputer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wired, optical fiber cable, radio frequency (RF), etc. or any suitablecombination thereof.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as JAVA, Smalltalk, C++, and Visual C++ or the like andconventional procedural programming languages, such as the C and Pascalprogramming languages or similar programming languages.

Aspects of the present invention may be described with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

Aspects of the described invention may be implemented in one or moreintegrated circuit (IC) chips manufactured withsemiconductor-fabrication processes. The maker of the IC chips candistribute them in raw wafer form (on a single wafer with multipleunpackaged chips), as bare die, or in packaged form. When in packagedform, the IC chip is mounted in a single chip package, for example, aplastic carrier with leads affixed to a motherboard or other higherlevel carrier, or in a multichip package, for example, a ceramic carrierhaving surface and/or buried interconnections. The IC chip is thenintegrated with other chips, discrete circuit elements, and/or othersignal processing devices as part of either an intermediate product,such as a motherboard, or of an end product. The end product can be anyproduct that includes IC chips, ranging from electronic gaming systemsand other low-end applications to advanced computer products having adisplay, an input device, and a central processor.

While the invention has been shown and described with reference tospecific preferred embodiments, it should be understood by those skilledin the art that various changes in form and detail may be made thereinwithout departing from the spirit and scope of the invention as definedby the following claims.

What is claimed is:
 1. A robotic finger assembly comprising: a fingerskeleton with one or more joints; a motor generating rotary motion of arotor; a twisted string comprised of a pair of cords, one end of thetwisted string being attached to the rotor and an opposite end of thetwisted string being coupled to the finger skeleton, the cords beingtwisted about each other for a first section of the twisted string anduntwisted for a second section of the twisted string; and a cord guidefixedly disposed between the cords, wherein the first section of thetwisted string is on a first side of the cord guide, the second sectionof the twisted string is on a second side of the cord guide, and rotarymotion of the rotor in one direction operates to twist the pair of cordson the first side of the cord guide while pulling a portion of the pairof cords from the second side of the cord guide into the first side ofthe cord guide.
 2. The robotic finger assembly of claim 1, wherein thecord guide comprises a pulley.
 3. The robotic finger assembly of claim1, further comprising a tendon passing through each of the one or morejoints of the finger skeleton, the tendon having a first end attached tothe finger skeleton and a second end coupled to the opposite end of thetwisted string.
 4. The robotic finger assembly of claim 1, furthercomprising a tendon having one end coupled to the opposite end of thetwisted string and a second end attached to a non-circular pulley. 5.The robotic finger assembly of claim 1, wherein a distance between thecord guide and the rotor of the motor remains constant throughout theoperation of the motor.
 6. The robotic finger assembly of claim 1,wherein the pair of cords can be foreshortened by approximately 86percent of an original length of the pair of cords before knotting inthe first section of the twisted string occurs.
 7. The robotic fingerassembly of claim 1, wherein the cord guide comprises a fixed pin.
 8. Arobotic finger assembly comprising: a finger skeleton with a pair ofpulleys having a common axis of rotation, each pulley having anon-circular shape; a motor for generating rotary motion of a rotor;first and second twisted string actuators each including a twistedstring coupled at one end to the rotor and attached at an opposite endto one of the non-circular pulleys, the twisted string actuators beingconfigured to operate in an antagonistic manner such that one twistedstring actuator lengthens the twisted string of that twisted stringactuator while the other twisted string actuator shortens the twistedstring of that twisted string actuator in response to rotary motionproduced by the motor, wherein the non-circular shape of the pulleys isadapted to keep both twisted strings in tension throughout a range ofthe rotary motion produced by the motor.
 9. The robotic finger assemblyof claim 8, further comprising a pair of tendons each having a first endcoupled to one of the non-circular pulleys and an opposite end attachedto the finger skeleton.
 10. The robotic finger assembly of claim 8,wherein the finger skeleton includes a joint, wherein the jointcomprises the pair of non-circular pulleys.
 11. The robotic fingerassembly of claim 8, further comprising a pair of idler pulleys disposedbetween the motor and the pair of non-circular pulleys, wherein thetwisted strings pass on opposite sides of the idler pulleys and crosseach other before attaching to the non-circular pulleys.
 12. The roboticfinger assembly of claim 11, wherein each twisted string comprises apair of cords twisted about each other for a first section of thetwisted string and untwisted for a second section of the twisted string,and wherein each twisted string actuator further comprises a cord guidefixedly disposed between the rotor and the idler pulleys, wherein thefirst section of the twisted string of each twisted string actuator ison a first side of the cord guide of that twisted string actuator, thesecond section of the twisted string of each twisted string actuator ison a second side of the cord guide of that twisted string actuator, androtary motion of the rotor in one direction operates to twist the pairof cords on the first side of the cord guide of a given one of thetwisted string actuators while pulling a portion of the pair of cords ofthat given one twisted string actuator from the second side of the cordguide of that given one twisted string actuator into the first side ofthe cord guide of that one twisted string actuator.
 13. The roboticfinger assembly of claim 12, wherein the cord guide comprises a fixedpin.
 14. The robotic finger assembly of claim 12, wherein the cord guidecomprises a pulley.
 15. The robotic finger assembly of claim 12, whereina distance between the cord guide and rotor of each twisted stringactuator remains constant throughout the operation of that twistedstring actuator.
 16. A twisted string actuator system comprising: amotor generating rotary motion of a rotor; a twisted string comprised ofa pair of cords, one end of the twisted string being attached to therotor and an opposite end of the twisted string being coupled to a load,the cords being twisted about each other for a first section of thetwisted string and untwisted for a second section of the twisted string;and a cord guide fixedly disposed between the cords, wherein the firstsection of the twisted string is on a first side of the cord guide, thesecond section of the twisted string is on a second side of the cordguide, and rotary motion of the rotor in one direction operates to twistthe pair of cords on the first side of the cord guide while pulling aportion of the pair of cords from the second side of the cord guide intothe first side of the cord guide.
 17. The twisted string actuator systemof claim 16, wherein the cord guide comprises a fixed pin.
 18. Thetwisted string actuator system of claim 16, wherein the cord guidecomprises a pulley.
 19. A twisted string actuator system comprising: amotor for generating rotary motion of a rotor; a pair of cams having acommon axis of rotation, each cam having a non-circular shape; first andsecond twisted string actuators each including a twisted string coupledat one end to the rotor and attached at an opposite end to one of thenon-circular cams, the twisted string actuators being configured tooperate in an antagonistic manner such that one twisted string actuatorlengthens the twisted string of that twisted string actuator while theother twisted string actuator shortens the twisted string of thattwisted string actuator in response to rotary motion produced by themotor, wherein the non-circular shape of the cams is adapted to keepboth twisted strings in tension throughout a range of the rotary motionproduced by the motor.
 20. The twisted string actuator system of claim19, further comprising a pair of idler pulleys disposed between themotor and the pair of cams having the non-circular shape, wherein thetwisted strings pass on opposite sides of the idler pulleys and crosseach other before attaching to the cams.